The present invention relates to an expandable honeycomb structure such as used for window coverings. The structure is made of two separate pleated materials which are secured together so that when expanded, they define a plurality of longitudinally extending cells, one on top of the other. In the retracted state of the honeycomb structure, the adjacent cells are collapsed on each other.
The prior art discloses various honeycomb structures made generally from a single piece of foldable material. Representative of such prior art are Rasmussen patents Re.30,254 and Re. 31,129, the patent to Masuda, U.S. Pat. No. 3,164,507, and the patent to Colson, U.S. Pat. No. 4,450,027. The prior art also includes honeycomb structures fabricated from separate sheets of material which are secured together to form individual cells. Representative of this prior art are the patents to Whitney, U.S. Pat. No. 1,827,718, Hartsell et al, U.S. Pat. No. 3,077,223, and the patents to Suominen, U.S. Pat. Nos. 4,288,485 and 4,388,354.
A difficulty with all of the prior art constructions is the ability to manufacture the honeycomb cells with opposite faces of different physical characteristics. This is sometimes desirable either for aesthetic of mechanical reasons. For example, thermal insulation against heat or cold, besides that given by the cell structure, can be provided by appropriate surfacing of the material of the structure which faces the elements. With the prior art constructions, as for example disclosed in the '027 patent, where a single piece of material is used to form the cells, different portions of the material which will ultimately define the opposite sides of the structure have to be separately processed prior to the formation of the honeycomb configuration. Problems of alignment of the differently treated surfaces can result in an inferior or unacceptable product. More particularly, the material must be fed accurately and folded accurately along its length. Also, it must be secured to the adjacent cell in such a way as to cover the line of demarcation separating the two differently treated surfaces. Otherwise, the different surfaces will show through from one side of the structure to the other.
With the honeycomb structures such as disclosed in the Suominen patents, different sheets of material are used to form the structure. These materials can obviously be made with different physical characteristics. However, this will not result in the opposite faces of the resulting honeycomb structure having different physical characteristics. This is so because of the method of manufacture. In Suominen, the materials are fed longitudinally and secured together longitudinally at spaced locations across the material. Therefore, in the expanded honeycomb structure, the opposite faces will be formed partially by one material and partially by the other material. Again, in order to have one entire side of the honeycomb structure provided with physical characteristics different from the other side, each material must be processed differently across its width in the same way as required with the single piece of material which is folded to form the cells of the honeycomb structure.
Another aspect of the honeycomb structures of the prior art relates to the creasing or pleating of the material forming each cell. One reason pleating is provided is to assist in the orderly collapsing of the individual cells as the structure is moved between an expanded and retracted position. Without pleats, the collapsing of the cells would tend to be haphazard and not give a neat appearance to the structure. In the cell construction disclosed in the '027 patent, the pleats are formed to be permanent so that the faces of the honeycomb structure extend in angular configuration in the expanded condition of the structure. If the pleats are not carefully and properly formed, they will tend to hang out. This is especially so after long, continued use of the structure, with the expanded condition being one where the cells lie one below the other. In such an orientation, the weight of the structure itself pulls on the material of the overlying cells with the greatest forces being exerted at the top of the structure by the entire weight of the underlying cells. Any falling out of the pleats tends to increase the overall height of the structure over the height as initially manufactured. The effect of this can be unpleasing and unsatisfactory, both aesthetically and physically.
The honeycomb structures disclosed in the prior art cited above may be made of very thin material where, for example, a translucent effect is desired. With very thin material care must be taken in the choice of adhesive that is used and the manner in which it is applied. This is important, not only from the manufacturing aspects, but also from the standpoint of durability of the resulting structure. With regard to manufacturing, too much adhesive or the wrong kind of adhesive and somewhat porous cell material can cause bleeding of the adhesive through the material. With the prior art structures where the secured materials are wound in layers upon each other, bleeding of adhesive through the material can cause successive layers to become adhered to each other so as to produce cells which are glued closed and will not normally open. This can either destroy the product or require extra procedures to separate the layers and open the cells. As far as durability is concerned, the adhesives chosen must, in many instances, be capable of withstanding the severe heat and sunlight when used in windows. The compatability of such adhesives which give proper durablity is not always the best as far as avoiding manufacturing bleedthrough problems.